Atocha, one of Madrid's major stations in the centre of the city, was the scene of the main attack.

"All hell broke loose, hundreds of police cars and helicopters everywhere.. and an endless procession of ambulances that continue to arrive at the scene even now as I type nine hours later," Mr Seal said.

Buildings shaken

One man, whose house is next to the railway line, told BBC News Online what happened:

"The second blast woke me up. My bed and the whole building moved and there was a huge sound. When I opened the window there was a smell of burning plastic and clouds of smoke," he said.

"When I went down the street I saw the train - six carriages with three big holes - some people were walking down the rails and many dead and injured were lying on the ground," he added.

You could hear people screaming, on the platform there were dead and injured, people were running covered in blood

Isabel Vega, student

"I saw many things explode in the air, I don't know, it was horrible," said civil servant Juani Fernandez, 50, on the platform at Atocha station when the blasts happened.

"People started to scream and run, some bumping into each other and as we ran there was another explosion.

"I saw people with blood pouring from them, people on the ground," he told the Associated Press news agency.